Heat exchangers are known which are adopted in boilers designed to heat a fluid, very commonly constituted by water or diathermic oil, which comprise, within a monolithic structure often made of aluminum, two opposite plates which have a variously shaped interspace for the conveyance of the fluid to be heated and are provided with pins which are inserted in a portion of space which is designed to convey the products of combustion, so as to receive heat which is transmitted to said fluid by means of the base of said pins.
In the particular case in which such exchangers are adopted in gas-fired condensing boilers, they have a burner which is located at the upper head, and the products of combustion are conveyed into a portion of space which extends from said head to the bottom of the exchanger, where there is a duct for evacuation to the stack.
The described heat exchangers are very widespread but have some disadvantageous characteristics. For example in the upper portion of the exchanger, close to the flame, short pins have to be used, to avoid burning them.